1. Field of the Invention
The present invention relates generally to an apparatus and a method for estimating a state of charge (SOC) of a battery, and more particularly to an apparatus and a method for estimating a state of charge (SOC) of a battery representing a non-linear characteristic by using a neural network.
2. Description of the Related Art
In general, a state of charge (SOC) of a battery represents a non-linear characteristic, so it is difficult to precisely detect the SOC of the battery. Thus, a value of SOC of the battery is not detected but estimated. Particularly, the SOC of batteries used for hybrid electrical vehicles (HEVs) or electric vehicles (EVs) having high C-rates may represent strong non-linear characteristic, so it is almost impossible to precisely detect the SOC of such batteries.
Conventionally, an Ah-counting (ampere hour counting) scheme, an OCV (open circuit voltage) measurement scheme, or a battery impedance measurement scheme has been used for estimating the SOC of the battery.
First, the Ah-counting scheme estimates the SOC of the battery by detecting an actual capacity of the battery. In this case, an estimation value of the SOC of the battery may depend on a state of a sensor used for detecting the actual capacity of the battery. Thus, the estimation value of the SOC of the battery may vary depending on the degree of preciseness and error of the sensor.
The OCV measurement scheme estimates the SOC of the battery based on an open circuit voltage of the battery. In this case, however, the SOC of the battery can be estimated only under a resting state of the battery. In addition, the OCV measurement scheme is influenced by external environment, such as an external temperature.
The battery impedance measurement scheme estimates the SOC of the battery based on an impedance value of the battery. However, the battery impedance measurement scheme is significantly influenced by an external temperature, so that reliability for the estimation value of the SOC of the battery may be lowered.
Therefore, it is necessary to provide a method for precisely estimating the SOC of the battery while minimizing an estimation error thereof regardless of an external temperature.